Bird flu is an infectious disease caused by strains of the Type A influenza viruses that ordinarily only infect birds. Avian influenza A (H5N1) virus infected and caused the deaths of people.
Bird flu, which is also known as avian influenza, was first identified in Italy more than 100 years ago. Avian viruses occur naturally in birds, and can infect birds including chickens, ducks, geese, turkeys, pheasants, quail, and guinea fowl. The avian influenza viruses generally do not infect humans.
Avian viruses are carried around the world by migratory birds. Wild ducks are natural reservoirs of the infection, according to the World Health Organization (WHO). Those wild birds generally don't become ill, but avian flu is extremely contagious and has caused some domesticated birds to become very ill and die. The casualties included chickens, turkeys, and ducks.
Reaction to the infection varies among the species because flu viruses are constantly mutating into new strains or subgroups. Low-pathogenic viruses cause few or no symptoms in infected birds. However, some strains can mutate into highly pathogenic avian influenza (HPAI) strains that are extremely infectious and deadly to birds.
The viruses are identified by a series of letters and numbers that refer to two proteins, hemagglutinin (HA) and neuraminidase (NA). There are 16 HA subtypes and nine NA subtypes of influenza A virus. Numerous combinations of the two proteins are possible, and each combination forms a new subtype.
There are 15 different Influenza A subtypes that can infect birds, according to the United States Centers for Disease Control (CDC). In comparison, there are three known subtypes of human flu virus A: H1N1, H1N2, and H3N2. Avian viruses can infect pigs, but people are generally not affected. That changed when there was an outbreak of H5N1 in Hong Kong in 1997.
The highly pathogenic H5N1 virus was first isolated in terns in South Africa in 1961, and then in Hong Kong in 1997. Hong Kong's avian flu outbreak coincided with 18 cases of severe respiratory disease in people. Those diagnosed with bird flu had close contact with poultry. Six people died, according to WHO. There was "limited transmission" of the virus to health care workers, but they did not become seriously ill.
Medical research showed that the avian virus had jumped from birds to people. Within three days, Hong Kong's poultry population of about 1.5 million birds was destroyed to prevent further infection. There was another H5N1 outbreak in Hong Kong in February of 2003. It affected two members of a family that had recently visited China. One person died, according to the WHO.
In the Netherlands in February of 2003, there was an outbreak of another highly pathogenic avian virus, H7N7. Two months later, a veterinarian died from the virus. It also caused mild illness in 83 people.
In Hong Kong, the avian virus subtype H9N2 caused mild cases of flu in two children in 1999 and one child in the middle of December of 2003, according to WHO. While H9N2 was not highly pathogenic in birds, there was an outbreak of H5N1 in Korea in mid-December of 2003. The next month, there was an outbreak in Vietnam that was followed by outbreaks in other Asian countries.
Human bird flu cases
The World Health Organization tracks bird flu outbreaks and the charts the numbers of human cases that have been confirmed by a laboratory. There were 74 cases and 49 deaths between January of 2004 and March 31, 2005. The flu caused two deaths in Cambodia. In Thailand, 12 of 17 people with bird flu died. In Vietnam, the flu was fatal in 35 of 55 diagnosed cases. Deaths related to the H5N1 viruses have been caused by pneumonia and pulmonary complications.
Moreover, the Democratic People's Republic of Korea (North Korea) officially reported the country's first outbreak of avian influenza in poultry on March 27, 2005. Outbreaks occurred at chicken farms, and there were no human cases at that time, according to WHO.
In October 2005, an outbreak of bird flu was reported at a farm near the Mongolian capital of Hohhot in the People's Republic of China. The H5N1 strain of the virus was detected in a parrot located in Britain. The parrot contracted the disease while in quarantine with birds originating in Taiwan. In January 2006, the H5N1 strain was confirmed as the cause of death in at least two cases in Dogubeyazit, Turkey. This case, as well as others documented in countries across Europe, indicate the potential for the disease to spread worldwide.
Preparing for a pandemic
The World Health Organization and nations including the United States are troubled about the deadly consequences that could occur if H5N1 mutated into a new virus subtype that could be transferred from one human to another. That subtype would develop if the avian virus acquired human influenza genes, according to the U.S. Department of Agriculture (USDA). A strain of bird flu spread by human-to-human contact could cause an influenza pandemic.
A pandemic is a worldwide epidemic that is dangerous because people have little or no immunity to the new virus strain. Historically, pandemics occur three to four times during a century when new virus subtypes appear. After World War I, the great influenza pandemic of 1917–1918 caused from 40 to 50 million deaths globally, according to WHO. The flu pandemic of 1968–1969 claimed 1 to 4 million lives.
According to a 2004 WHO report, medical influenza experts agree that another flu pandemic is "inevitable and possibly imminent." In a December 8, 2004 report, WHO warned that the "best case scenario" projection for next pandemic was that the new flu strain would kill from 2 to 7 million people. Moreover, "tens of millions" of people would require medical attention. The appearance of H5N1 signals that the world is moving closer to a pandemic, WHO reported.
The spread of H5N1 to humans increased the likelihood of a new strain emerging that could be transmitted by people. That could create a pandemic. Nations and the World Health Organization are working to prevent a pandemic or cause it to be less deadly. Their strategies include efforts to decrease the spread of flu strains in poultry and the development of vaccines to treat the virus in people.
Causes and symptoms
Avian flu is caused by an influenza virus that birds carry in their intestines. The virus spreads as infected birds excrete saliva, nasal secretions, and feces. Birds vulnerable to the flu become infected when they come into contact with the excretions or surfaces contaminated by the infected matter.
Birds that survive the H5N1 infection can excrete the virus for at least 10 days, according to a WHO report. The strain had proliferated through bird-to-bird contact to flocks on farms and poultry in live bird markets. The virus can also spread in surfaces including manure, bird feed, equipment, vehicles, egg flats, and crates, and the clothing and shoes of people who came into contact with the virus.
A small amount of a highly pathogenic avian influenza virus could be deadly. One gram (0.035 ounces) of contaminated manure could hold enough virus to infect 1 million birds, according to the USDA. From 1997 through the spring of 2005, the viruses primarily infected people in Asia who had contact with infected birds and surfaces.
Bird flu symptoms in people
In early 2005, information about symptoms of H5N1 in humans was based on the 1997 Hong Kong outbreak. People experienced traditional flu symptoms such as a fever, cough, sore throat, and aching muscles. Other symptoms included eye infections (conjunctivitis ), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.
Avian flu symptoms in birds
The sudden death of a bird that had not appeared ill is one symptom of the highly pathogenic bird flu. According to the USDA, infected live birds may display one or more of the following symptoms: lack of energy, appetite loss, nasal discharge, coughing, sneezing, a lack of coordination, and diarrhea. In addition, the bird may lay fewer eggs or produce eggs that are soft-shelled or misshapen. Furthermore, there may be swelling of the head, eyelids, comb, and wattles. Another symptom is purple discoloration on the combs, wattles, and legs.
If there is an outbreak of the highly pathogenic flu in birds, they are destroyed to prevent the spread of the virus.
Virus mixing vessels
Influenza viruses undergo frequent changes and form new subtypes. In addition, influenza A viruses can trade genetic materials with the viruses of other species. Two different strains trade or merge material, a process known as an antigenic shift. That shift produces a new subtype that is different from the two parent viruses. When the new subtype contains genes from the human virus, a pandemic resulted because there was no immunity to the virus and no vaccine to protect against it.
The genetic shift occurs in a "mixing vessel" that was susceptible to both types of flu. In the past, the shift was thought to be related to people living close to pigs and domestic poultry. Pigs can be infected by avian viruses and mammalian viruses like the human strains, according to WHO. However, research into the H5N1 strain indicates that people can serve as the mixing vessels. As more people become infected with bird flu, the probability increases that humans would serve as the mixing vessel for a new subtype that could be transmitted from one person to another.
The symptoms of avian flu and human flu are very similar, so laboratory testing is needed to diagnose avian influenza. In addition to diagnosing the individual, testing in 2005 was performed to determine whether the infection was spreading from birds to people or from humans to humans.
Diagnostic tests for human flu are rapid and reliable, according to WHO. The international organization noted that laboratories within WHO's global network have high-security facilities and experienced staff. Test methods include a viral culture that analyses a blood sample and swabbings of the nose or throat. Other testing examines respiratory secretions.
In the United States, the Centers for Disease Control is among the organizations preparing for a possible outbreak of bird flu in humans. In addition to specifics related to diagnosing bird flu, CDC refers healthcare workers to precautions to prevent the spread of flu and other respiratory infections in medical settings.
Precautionary measures include directing people to observe cough etiquette. People with symptoms of respiratory infection should cover their mouths or use facial tissues when coughing or sneezing. After coughing or sneezing, the person should wash their hands with a non-antimicrobial soap and water, alcohol-based hand rub, or antiseptic handwash.
Furthermore, people with flu-like symptoms may be given masks to wear while they are waiting to be examined by medical personnel. The healthcare workers should wear masks in some circumstances. Undoubtedly, they will wear masks when working with people with symptoms of bird flu.
As of March of 2005, there was no vaccine to protect people from the H5N1 virus, according to the CDC. However, the U.S. agency and the World Health Organization had isolated seed strains of the virus in order to make a vaccine. Safety tests were scheduled to start in April of 2005 on a vaccine manufactured by Sanofi pasteur, a firm in Swiftwater, Pennsylvania, formerly known as Aventis Pasteur.
On March 23, 2005, the National Institute of Allergy and Infectious Diseases (NIAID) announced that fast-track recruitment had started for volunteers to participate in an investigative study of the vaccine. During the Phase I trial, the trial vaccine will be tested on 450 healthy adults between the ages of 18 to 64, according to NIAID, which is part of the National Institutes of Health.
Studies were to be conducted at University of California at Los Angeles, University of Maryland School of Medicine in Baltimore, and the University of Rochester School of Medicine and Dentistry, Rochester, New York. If the vaccine is proven safe for adults, there were plans to test it in people in other age groups such as children and the elderly.
Furthermore, research was underway on a vaccine to fight H9N2, another avian flu virus subtype.
Treatment with existing drugs
Existing anti-viral medications may sometimes be effective against avian flu viruses, according to a March 18, 2005, report from CDC. In the United States, four drugs have been approved by the U.S. Food and Drug Administration (FDA) for the treatment and prevention of influenza A viruses.
The medications amantadine (Symmetrel), rimantadine (Flumadine), seltamivir (Tamiflu), and zanamivir (Relenza) were clinically effective in the treatment of influenza A viruses in otherwise healthy adults.
However, avian flu research indicated that the H5N1 virus was resistant to amantadine and rimantadine, according to CCDC. The other two drugs would "probably work," according to CDC. However, studies were needed of the medication's effectiveness.
During the 2004 human flu season in the United States, the Associated Press reported that Relenza cost about $55 for the typical 10-day treatment. Tamiflu cost approximately $66 for the same course of treatment. Insurance frequently covered part of the prescription costs.
For people diagnosed with bird flu, the World Health Organization recommends that patients take Tamiflu twice daily for five days. Treatment should begin as soon as possible. Patients may also receive medication to lower fevers and antibiotics to fight secondary infections.
In the spring of 2005, there was no H5N1 vaccine. Countries including the United States were reportedly stockpiling Tamiflu in the event a pandemic erupted. At that time, WHO and CDC recommended the issuing of anti-viral medication as a preventive measure to people working in poultry production. Those people, along with health care workers, would have priority for the medications.
In March of 2005, people in South Korea began eating more kimchi to ward off avian flu infection, according to the reports from the British Broadcasting Company and other news organizations. The public turned to the spicy vegetable dish after scientists at Seoul National University announced that kimchi aided in the recovery of 11 out of 13 infected chickens. The scientists fed the birds an extract of kimchi, a dish made by fermenting cabbage with red peppers, radishes, and large amounts of garlic and ginger. A week later, all but two birds showed signs of recovery.
The researchers acknowledged that their study was unscientific. At that time, they were not sure how or why kimchi was related to the recovery. However, the announcement led people to again regard kimchi as a health remedy. In 2003, interest in kimchi increased when people thought eating it helped prevent SARS (severe acute respiratory syndrome). No scientific confirmation was made between kimchi and SARS prevention.
Bird flu has been fatal to people, and there was concern in 2005 about the virus mutating into a strain that could be transmitted by people. Health organizations and government agencies focused on preventing or reducing the risks of a pandemic caused by bird flu.
In the United States, research was underway on vaccines to fight the flu. Other efforts include the USDA Safety's guidelines for people working with poultry. Strategies included trade restrictions on poultry and poultry products from Asia, according to the USDA. Imported live birds and eggs were quarantined for 30 days. During that time, they were tested for bird flu and exotic Newcastle disease. The United States bans the import of poultry meat from Asia because meat processing plants were not approved by the USDA's Food Safety and Inspection Service.
In the spring of 2005, bird flu was primarily a risk for people in the United States who worked with poultry. Potentially vulnerable people included those working with poultry on farms and avian health workers like veterinarians. People working with birds in locations such as commercial poultry facilities, veterinary offices, and live bird markets should wear protective clothing. That equipment includes boots, coveralls, face masks, gloves, and headgear, according to the USDA. If necessary, they should receive antiviral medications as a safeguard.
Furthermore, poultry producers should implement security measures to prevent the outbreak of a highly pathogenic virus. Those actions include keeping flocks away from wild or migratory birds and providing clothing and disinfectant facilities for employees. Plastic crates should be used at live bird markets because they were easier to clean than wood crates. Cleaning and disinfecting areas were also important for preventing an outbreak.
If necessary birds would be quarantined or destroyed.
Associated Press. "Bird Flu Called Global Human Threat: Asia Outbreak Poses 'Gravest Possible Danger,' U.N. Official Says, Urging Controls." Washington Post. February 24, 2005 [cited March 30, 2005] 〈http://www.washingtonpost.com/wp-dyn/articles/A46424-2005Feb23.html〉.
World Health Organization. Regional Office for the Americas. 525, 23rd Street NW, Washington, DC 20037. 202-974-3000. 〈http://www.who〉.
Highly Pathogenic Avian Influenza. United States Department of Agriculture Animal and Plant Inspection Safety. March 2004 [Cited March 31, 2005]. 〈http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_ahavianflu.html〉.
Avian Influenza. World Health Organization. Continuously updated [cited March 31, 2005]. 〈http://www.who.int/csr/disease/avian_influenza/en/〉.
Chazan, David. "Korean dish 'may cure bird flu.'" BBC News. March 14, 2005 [cited March 30, 2005]. 〈http://news.bbc.co.uk/go/pr/fr/-/2/hi/asia-pacific/4347443.stm〉.
Focus on the Flu. National Institute of Allergy and Infectious Diseases. Continuously updated [cited March 31, 2005]. 〈http://www2.niaid.nih.gov/Newsroom/FocusOn/Flu04/〉.
Influenza (commonly known as flu) is a highly contagious illness caused by a group of viruses called the orthomyxoviruses. Infection with these viruses leads to a self-limiting illness usually characterized by fever, muscle aches, fatigue, and upper respiratory infection and inflammation . Children and young adults usually recover from influenza within 3–7 days with no complications; however, in older adults, especially those over 65 with underlying conditions such as heart disease or lung illnesses, influenza can be deadly. Most of the hospitalizations and deaths from influenza occur in this age group. Although an influenza vaccine is available, it does not confer complete protection against all strains of influenza viruses.
Like all viruses, orthomyxoviruses cause illness by entering host cells and replicating within them. The new viruses then burst from the host cell and infect other cells. Orthomyxoviruses are sphere-shaped viruses that contain ribonucleic acid (RNA ). The viruses use this RNA as a blue-print for replication within host cells. The outer envelope of an orthomyxovirus is studded with protein spikes that help the virus invade host cells. Two different types of spikes are present on the virus's outer envelope. One type, composed of hemagglutinin protein (HA), fuses with the host cell membrane, allowing the virus particle to enter the cell. The other type of spike, composed of the protein neuraminidase (NA), helps the newly formed virus particles to bud out from the host cell membrane.
The only way a virus can be neutralized and stopped is through the body's immune response. At the present time, no cure or treatment is available that completely destroys viruses within the body. The HA spikes and proteins in the orthomyxovirus envelope stimulate the production of antibodies, immune proteins that mark infected cells for destruction by other immune cells. In a healthy person, it takes about three days for antibodies to be formed against an invading virus. People with impaired immune function (such as people with Acquired Immune Deficiency Syndrome, the elderly, or people with underlying conditions) may not be able to mount an effective immune response to the influenza virus. Therefore, these people may develop serious complications, such as pneumonia , that may lead to hospitalization or death.
Three types of orthomyxoviruses cause illness in humans and animals: types A, B, and C. Type A causes epidemic influenza, in which large numbers of people become infected during a short period of time. Flu epidemics caused by Type A orthomyxoviruses include the worldwide outbreaks of 1918, 1957, 1968, and 1977. Type A viruses infect both humans and animals and usually originate in the Far East, where a large population of ducks and swine incubate the virus and pass it to humans. The Far East also has a very large human population that provides a fertile ground for viral replication. In 1997, a new strain of influenza A jumped from the poultry population in Hong Kong to the human population. H5N1, as the strain was named, was contracted through contact with the feces of chicken. The illness it caused (dubbed avian flu) was severe, and sometimes fatal. Although it was strongly believed that humans could not get the disease from eating properly cooked chicken, the decision was ultimately made to destroy and bury all of the chickens in Hong Kong. This massive effort was carried out in December 1997.
Type B influenza viruses are not as common as type A viruses. Type B viruses cause outbreaks of influenza about every two to four years. Type C viruses are the least common type of influenza virus and cause sporadic and milder infections.
The hallmark of all three kinds of influenza viruses is that they frequently mutate. Due to the small amount of RNA genetic material within a virus, mutation of the genetic material is very common. The result of this frequent mutation is that each flu virus is different, and people who have become immune to one flu virus are not immune to other flu viruses. The ability to mutate frequently therefore allows these viruses to cause frequent outbreaks.
Influenza is characterized by a sudden onset of fever, cough, and malaise. The incubation period of influenza is short, only 1–3 days. The cells that the influenza virus target are the cells of the upper respiratory tract, including the sinuses, bronchi, and alveoli. The targeting of the upper respiratory tract by the viruses accounts for the prominence of respiratory symptoms of flu. In fact, flu viruses are rarely found outside the respiratory tract. Most of the generalized symptoms of flu, such as muscle aches, are probably due to toxin-like substances produced by the virus.
Symptoms last for about 3–6 days; however, lethargy and cough may persist for several days to weeks after a bout with the flu. Children may have more severe symptoms due to a lack of general immunity to influenza viruses. Children also have smaller airways, and thus may not be as able to compensate for respiratory impairment as well as adults.
The most common complication of influenza is pneumonia. Pneumonia may be viral or bacterial. The viral form of pneumonia that occurs with influenza can be very severe. This form of pneumonia has a high mortality rate. Another form of pneumonia that is seen with influenza is a bacterial pneumonia. If the respiratory system becomes severely obstructed during influenza, bacteria may accumulate in the lungs. This type of pneumonia occurs 5–10 days after onset of the flu. Because it is bacterial in origin, it can be treated with antibiotics .
Other complications of influenza include infections of the heart and heart lining, infections of the brain, and Guillain-Barre syndrome (GBS). GBS is a paralytic disease in which the body slowly becomes paralyzed. Paralysis starts in the facial muscles and moves downward. GBS is treated symptomatically and usually resolves by itself. Another complication of influenza is Reye's syndrome. Occurring typically in children, Reye's syndrome is associated with aspirin intake during an attack of influenza. Reye's syndrome is characterized by nausea, vomiting, and progressive neurological dysfunction. Because of the risk of Reye's syndrome, children should not be given aspirin if they have the flu. Non-aspirin pain relievers, such as acetaminophen, should be given instead of aspirin.
Flu is treated with rest and fluids. Maintaining a high fluid intake is important, because fluids increase the flow of respiratory secretions, which may prevent pneumonia. Antiviral medications (amantadine, rimantadine) may be prescribed for people who have initial symptoms of the flu and who are at high risk for complications. This medication does not prevent the illness, but reduces its duration and severity.
A flu vaccine is available that is formulated each year against the current type and strain of flu virus. The virus is grown in chicken eggs, extracted, and then rendered noninfective by chemicals. The vaccine is also updated to the current viral strain by the addition of proteins that match the current strain's composition. The vaccine would be most effective in reducing attack rates if it was effective in preventing influenza in schoolchildren; however, in vaccine trials the vaccine has not been shown to be effective in flu prevention in this age group. In certain populations, particularly the elderly, the vaccine is effective in preventing serious complications of influenza and thus lowers mortality.
Vaccine research is ongoing. One of the more exciting advances in flu vaccines involves research studies examining an influenza vaccine mist, which is sprayed into the nose. This is predicted to be an excellent route of administration, which will confer even stronger immunity against influenza. Because it uses a live virus, it encourages a strong immune response. Furthermore, it is thought to be a more acceptable immunization route for schoolchildren, an important reservoir of the influenza virus.
See also Flu: The great flu epidemic of 1918; Viruses and responses to viral infection